Data Encryption Standard (DES) is a symmetric key algorithm. Originally developed by IBM, under project name Lucifer, this 128-bit algorithm was accepted by the NIST in 1974, but the key size was reduced to 56 bits, plus 8 bits for parity. It somehow became a national cryptographic standard in 1977, and an American National Standard Institute (ANSI) standard in 1978. DES was later replaced by the Advanced Encryption Standard (AES) by the NIST. All other options are asymmetric algorithms. Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 8: Cryptography (page 525). Reference: DES: http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf